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FERTILISERS (GENERAL METHODS)                  123

inner one with, two lateral orifices ; the conical flask C contains 20-25 c.c.
(exact amount) of N/2-sulphuric acid and the safety tube D a little water.

When 200-250 c.c. of liquid have distilled over, the flask C and tube D
are detached, the latter being washed into the flask and the contents of the
latter titrated with N/2-sodium hydroxide in presence of methyl orange.
The number of c.c. of N/2-acid neutralised, multiplied by 0-007, gives the
amount of nitrogen in grams in the weight of substance taken for analysis.
In cases where ammoniacal nitrogen is present as well as organic nitrogen,
the result just obtained must be diminished by that obtained by method (A}.

D. Total Nitrogen.—The preceding methods give the total nitrogen
where this is all of one form or a mixture of ammoniacal and organic. If,
besides these two, nitric nitrogen is also present, the total nitrogen is deter-
mined as follows :

Jodlbaur's modification of the Kjeldahl method. From I to 5 grams of
substance l are well mixed in a Kjeldahl flask with 20 c.c. of phenol-sulphuric
acid solution (40 grams of phenol dissolved in I litre of sulphuric acid of
66° Baume) and, after 5 minutes, 2-3 grams of zinc dust are added in small
portions and with cooling. The flask is then heated over a small flame for
10-15 minutes, allowed to cool and 5 c.c, of phosphosulphuric acid (see under
C}, a little copper oxide and a few drops of platinic chloride solution added,
the subsequent procedure being as in the Ulsch method (see under C).

The official Italian methods conform to those given above, but they allow
also : (i) for nitric nitrogen, of the use of Ulsch's method, which consists in
reduction of nitrates to ammonia by means of reduced iron or zinc, and of
Devarda's method, in which the reduction is effected by aluminium or zinc in
alkaline solution ; (2) for the total nitrogen of the use of Dumas' method.

4. Determination of the Phosphoric Acid

Determinations may be required of the total phosphoric acid, of that
soluble in water, and of that soluble in ammonium citrate. Here is described
only the method for the total phosphoric acid, applicable to all phosphatic
fertilisers except Thomas slag (q.v.). Estimation of the phosphoric acid
soluble in water or in citrate, applicable essentially to superphosphates and
other slags, is treated later in dealing with these products in particular.

Determination of the Total Phosphoric Acid.—The following solu-
tions are required :

(a)  Ammonium citrate.    400 grams of crystallised citric acid are covered
with water and neutralised with   ammonia  (D = 0-92)  (about   500   c.c.
required), the liquid being cooled meanwhile and finally made up to I litre.

(b)  Magnesia Mixture,    no grams of crystallised magnesium chloride,
140 grams of ammonium chloride, 700 c.c. of 8% ammonia (D = 0-967)
and 1300 c.c. of water.

(c)  Ammonia, D^= 0-920.

PROCEDURE. Five grams of the substance are boiled for about 30
minutes in a 250 c.c. measuring flask with 50-75 c.c. of water, 20 c.c. of

1 If this is moist or difficult to attack, it is well to add 2-3 grams of finely powdered
burnt gypsum.carbon dioxide.    If the fertiliser contains oxalic acid